Comparison of the reactivity of bis(mu-oxo)Cu(II)Cu(III) and Cu(III)Cu(III) species to methane.

Methane hydroxylation at the dinuclear copper site of particulate methane monooxygenase (pMMO) is studied by using density functional theory (DFT) calculations. The electronic and structural properties of the dinuclear copper species of bis(mu-oxo)Cu(II)Cu(III) and Cu(III)Cu(III) are discussed with respect to the C-H bond activation of methane. The bis(mu-oxo)Cu(II)Cu(III) species is highly reactive and considered to be an active species for the conversion of methane to methanol by pMMO, whereas the bis(mu-oxo)Cu(III)Cu(III) species is unable to react with methane as it is. If a Cu-O bond of the bis(mu-oxo)Cu(III)Cu(III) species is cleaved, the resultant Cu(III)Cu(III) species, in which only one oxo ligand bridges the two copper ions, can activate methane. However, its energetics for methane hydroxylation is less favorable than that by the bis(mu-oxo)Cu(II)Cu(III) species. The DFT calculations show that the bis(mu-oxo)Cu(II)Cu(III) species is more effective for the activation of methane than the bis(mu-oxo)Cu(III)Cu(III) species. The reactive bis(mu-oxo)Cu(II)Cu(III) species can be created either from the electron injection to the bis(mu-oxo)Cu(III)Cu(III) species or from the O-O bond cleavage in the mu-eta(1):eta(2)-peroxoCu(I)Cu(II) species.